The present invention relates to a magnetic head assembly for use in magnetic disk apparatuses.
A magnetic had assembly for use in a hard disk apparatus or a floppy disk apparatus includes a slider and a gimbal spring.
The slider is an extremely hard member highly resistent to wear. Typical slider materials include sintered metallic oxide such as ceramics and ferrites. An electromagnetic transducer element is attached to the slider for converting electric signals into magnetization and vice versa. The slider itself may also constitute part of the electromagnetic converter. The slider is fixed to the gimbal spring with an adhesive.
The gimbal spring is an elastic metallic member. The gimbal spring, typically made of stainless steel, holds the slider over a magnetic recording medium.
The gimbal spring positions the slider on/above the slider against the magnetic recording medium. Therefore, when the magnetic recording medium is stationary, the slider is in contact with the recording medium. When the magnetic recording medium begins rotating, the slider glides over the medium and it takes off the medium to fly. When the magnetic recording medium is rotating, the slider flies over the recording medium keeping a small gap between the slider and the disk. When the recording medium stops, the slider again comes into contact with the magnetic recording medium.
The usual shape of the slider is illustrated in FIG. 1. A slider 10 is secured to a gimbal spring 20. The slider 10 has flying surfaces 11 and 12.
Referring now to FIG. 2, the flying surfaces 11 and 12 are formed to be slightly convex. These convex faces are called "crown". The crown height C here refers to the distance C between the straight line connecting the terminal points X and Y of the flying surfaces 11 or 12 and the point Z on the flying surfaces 11 or 12 where the distance from the straight line is the greatest. When the flying surface is 2 mm long and 0.3 mm wide, the crown height C is about 0.010-0.050 .mu.m.
The crown prevents the slider from sticking to the media. The crown also serves to shorten the gliding distance at a time of disk start and stop and contributes to increasing the durability of the medium.
As shown in FIG. 1, at the fore ends of the flying surfaces 11 and 12 in the direction of the disk's movement are formed chamfered portions 15 and 16 at an angle of about 30 minutes. The chamfered portions 15 and 16 produce flying pressure particularly when the disk speed is low.
In order to read/write signals properly, the flying attitude of the slider 10 should be kept stable so that distance between the transducer and the media is kept constant. The flying attitude of the slider 10 are affected by the shape of the flying surfaces 11 and 12. Therefore, in order to keep the flying attitude of the flying slider 10 constant, the shape of the flying surfaces 11 and 12, i.e. The shape of the crown, should be kept constant under every possible operating condition.
However, the crown is significantly deformed by a thermal change. This crown deformation can be assessed by a change in the crown height C. The varying rate of the crown height C by a thermal change may exceed 50%.
An example of a technique to restrain the deformation of the crown by a thermal change (hereinafter referred to as "the prior art technique") is described in Japanese Utility Model Laid-open No. 133362 of 1989.
The prior art technique presumes that the deformation of the magnetic head results from the difference in the thermal expansion coefficient between the slider material and that of the gimbal spring. The slider material is attached (e.g. glued) to the gimbal spring at an elevated temperature. After the glue is cured, the slider material and the gimbal spring are cooled to room temperature. If the thermal expansion difference between the slider material and the gimbal spring is significant, the slider material deforms because of the temperature difference between before and after the gluing.
The prior art technique reduces the magnetic head deformation by equalizing the thermal expansion coefficient of the slider material and that of the gimbal spring. Specifically, according to the prior art technique, alumina carbide titanate (Al.sub.2 O.sub.3 TiC) is used as the material for the magnetic head, and 43 wt % Ni, as that for the gimbal spring. In this case, the thermal expansion coefficients of the magnetic head and the gimbal spring are substantially identical at 7.9.times.10.sup.-6.
However, experiments have revealed that the prior art technique cannot reduce the magnetic head deformation sufficiently. This experiment will be hereinafter referred to as experiment #0. In experiment #0, the slider was made of alumina carbide titanate and the gimbal spring was made of 42 alloy containing 42 wt % of Ni.
Before experiment #0, the thermal expansion coefficient of the slider was measured, and the result is shown in FIG. 3. In this test, the thermal expansion coefficients of six samples were measured at 10.degree. C. intervals. The average of the measurements demonstrated that the thermal expansion coefficient of the slider was about 5.7.times.10.sup.-6 in the temperature range of 0.degree. C. to 80.degree. C.
On the other hand, the thermal expansion coefficient of the gimbal spring was 6.0.times.10.sup.-6.
Thermal expansion coefficient difference D between the slider and the gimbal spring was about 5%. The thermal expansion coefficient difference D is defined as ((E1/E2)-1).times.100, where E1 and E2 are the thermal expansion coefficient of the gimbal spring and the slider, respectively. The thermal expansion coefficient difference of 5% means that the thermal expansion coefficient of the slider and that of the gimbal spring are substantially identical.
The results of experiment #0 are illustrated in the chart of FIG. 4.
In the graph of FIG. 4, the horizontal axis represents the temperature, and the vertical axis represents the crown height C. The solid circles indicate measurements when the temperature is rising. The open circles indicate measurements when the temperature is falling. In this experiment, after the crown height C was measured while increasing the temperature from about 20.degree. C. to 40.degree. C., it was measured again while decreasing the temperature to 20.degree. C. This two-way process is defined to be one trial. The measurements in a trial are linked by curves in the graph. In the experiment, three sliders each having different crown heights by about 10 nm were subjected to the trial, with results corresponding to the three curved lines being illustrated in FIG. 11.
According to experiment #0, the average variation of the crown height C per 20.degree. C. temperature change was 8 nm, which reveals that the prior art technique cannot sufficiently reduce the crown deformation.